The present invention relates to a radio communication system and-more particularly to a radio communication method and apparatus for carrying out a channel notification in a digital mobile communication system.
As one of the digital radio communication systems being put to practical use currently, a mobile communication system is defined in “REGIONAL DIGITAL MOBILE TELECOMMUNICATION SYSTEM”, ARIB STD-T79, Ver. 1, Association of Radio Industries and Businesses, Jun. 6, 2001, pp. 1-24. FIG. 11 illustrates a general mobile communication system having a plurality of base station zones. In FIG. 11, numeral 1101 denotes a line controller, 1102-1 and 1102-2 base stations and 103-1 and 1103-2 base station zones, that is, communication areas of the respective base stations. The mobile communication system is so configured that the base station 1102-1 makes communication connection service with a plurality of mobile stations 1104-1, 1104-2, . . . , 1104-N residing in the communication area 1103-1 between the base stations or between the mobile stations via base station or directly between the mobile stations or makes communication connection service between a mobile station outside the communication area 1103-1 and another mobile station within the communication area 1103-1.
The mobile communication system is also so configured that the base station 1102-2 makes communication connection service with a plurality of mobile stations 1105-1, 1105-2, . . . , 1105-M residing in the communication area 1103-2 between the base stations or between the mobile stations via base station or directly between the mobile stations or makes communication connection service between a mobile station outside the communication area 1103-2 and another mobile station within the communication area 1103-2. The mobile stations are named generically as the mobile station 1104 or 1105.
The line controller 1101 makes communication connection between the base stations and the plurality of mobile stations, maintenance and management of the service area in the digital radio communication system and controls an originating call from a mobile station or setting of communication routes. The line controller 1101 may be installed integrally with the base station 1102-1 or 1102-2 or separately from the base stations as shown in FIG. 11. In the latter case, the line controller 1101 is generally connected to the base stations 1102-1 and 1102-2 via transmission paths 1106-1 and 1106-2 such as cable or microwave communication lines. Further, the mobile stations described here contain radios or radio transmitter-receivers mounted in vehicles, portable radios and information terminal stations. In this example, only two base stations are shown, although in general the system includes a plurality of base stations and a large number of mobile stations but description is made with reference to FIG. 11 showing the most simple configuration for convenience of description.
FIG. 5 shows an example of assignment of frequencies for radio carriers permitted to be used in the digital mobile communication system using the digital radio technique defined in the standard ARIB STD-T79. In FIG. 5, in the uplink direction, that is, in the direction of transmission from the mobile station to the base station, 112 waves (f1, f2, . . . ) having a bandwidth of 25 KHz have been authorized for radio carriers f of about 262 to 266 MHz. Further, in the downlink direction, that is, in the direction of transmission from the base station to the mobile station, 112 waves (F1, F2, . . . ) having a bandwidth of 25 KHz have been authorized for radio carriers F of about 271 to 275 MHz separated by 9 MHz from 262 MHz in the uplink direction. Accordingly, the frequencies f1, f2, . . . and F1, F2, . . . can be used in the uplink and downlink directions, respectively, in communication of the digital radio communication system. The systems can use one or a plurality of radio carriers in accordance with the respective system scale. Further, in the standard ARIB STD-T79, a radio carrier W has been authorized so that a mobile station 1104 positioned within the communication area 1103 can make direct communication with a mobile station 1104 positioned outside of the communication area 1103. The radio carrier W also has a bandwidth of 25 KHz and over ten waves (W1, W2, . . . ) have been authorized. In the radio communication system shown in FIG. 11, for example, the base station 1102-1 makes communication using pair waves of f1 in the uplink direction and F1 in the downlink direction and the base station 1102-2 also makes communication using pair waves of f3 in the uplink direction and F3 in the downlink direction.
Further, each radio carrier is divided into frames as shown in FIG. 6 and each frame is further divided into four slots, to which a control channel C and communication channels S1, S2 and S3 are assigned. The communication channels S1, S2 and S3 are named collectively as communication channel S. One frame is 40 ms, for example. The control channel C is used to make connection control of radio communication line and the communication channel S is used to make talking and data communication.
JP-A-5-191856 discloses a method in which a number-of-calls counter for counting the number of originating calls and the number of calls that cannot attain connection due to the fact that communication channel is busy is provided in the radio base station and the numbers are broadcast to portable terminals (radio terminals) at all times or when connection cannot be attained in origination of call by each portable terminal.
JP-A-2005-136779 discloses a mobile communication system including a plurality of base stations. The system includes retrieval means for retrieving idle channel for each base station periodically to obtain idle channel information, information sharing means for notifying the idle channel information to other base stations to share the idle channel information with each other, and idle channel information notification means for notifying the idle channel information of other base stations to mobile terminals on the basis of the shared idle channel information.
Reference may be further made to JP-A-2003-250176 and JP-A-6-303662.